Various liquid beverages are customarily filtered in the manufacturing process. For example, beer transferred from a fermentor to storage is known as ruh beer and contains suspended protein solids and yeast cells which need be removed by filtration. Ruh beer generally contains from 10.sup.7 to less than 10.sup.6 cells per milliliter, but will vary depending on the brewing process used. Ruh beer is partially carbonated and is filtered through a filter screen after a filter aid has been applied to the screen.
Brewers and other processors often filter beer and other beverages through a fine mesh screen precoated with a filter aid such as diatomaceous earth or silicic acid. Diatomaceous earths in contact with liquids are known to transfer soluble iron to the liquids. If the transfer of iron is to be avoided, specially treated filters may be used such as described in U.S. Pat. Nos. 4,202,910 and 4,134,857. Specially treated silicon dioxide particles are also sometimes used as a filter aid. These materials are prepared and used as described in U.S. Pat. Nos. 4,647,464 and 4,457,900. The filtered beer should be clear to the eye. Moreover, the filtered beer should have the same clarity and organoleptic aspects after pasteurizing as a beer processed through diatomaceous earth.
The pore size of filter screens used to filter beverages such as beer may vary from one producer to another but is frequently on the order of 60 microns. A diatomaceous earth such as Hyflo-Super-Cel, manufactured by Johns Manville Corporation, is frequently used as a precoating material for the filter screens used in beer breweries. Such filter aids or precoating materials, after use, are a waste material and pose a disposal problem.
A typical analysis of a diatomaceous earth filter aid commonly used for beer production is:
pH: 10.0 PA0 Water solubles, %: 0.15 PA0 Iron (as Fe.sub.2 O.sub.3), %: 1.5
Beer, wine and many juices have a pH of 4.5 or lower, and there is evidence that iron present in the filter aid is solubilized in such acidic liquids. In the instance of beer, iron has been known to have a negative effect on clarity and flavor.